Is it worth to perform initial non-operative treatment for patients with acute ACL injury?: a prospective cohort prognostic study

Park et al. Knee Surgery & Related Research           (2021) 33:11                                                                     Knee Surgery
                                                                                                                                       & Related Research

 RESEARCH ARTICLE                                                                                                                                   Open Access

Is it worth to perform initial non-operative
treatment for patients with acute ACL
injury?: a prospective cohort prognostic
Yong-Geun Park1, Chul-Won Ha2,3,4* , Yong-Beom Park5, Sang-Eun Na6, Manyoung Kim7, Tae Seon Kim1 and
Yong Yeon Chu1

  Purpose: To evaluate the result of implementing an initial non-operative treatment program for an acute ACL
  injury and to find if the timing of initiating the non-operative treatment is significant.
  Methods: This study included a prospective cohort of 85 consecutive patients with acute ACL injury who were
  treated according to the above strategy for the initial 3 months with 1-year follow-up. Clinical evaluations were
  made by Lysholm score, Tegner activity score, Lachman test (LT), pivot-shit test (PST), and the side to side
  difference (SSD) by KT-2000 arthrometer. The results were analyzed according to the timing of initiating the non-
  operative treatment.
  Results: Initially, 84% of the patients showed LT and PST ≤ grade 1, and 16% with ≥grade 2. At 1-year follow-up, 77
  patients (91%) with LT and PST ≤ grade 1 did not receive reconstruction as copers and 8 patients with LT or PST ≥
  grade 2 required reconstruction (six patients received the operation and two refused). The patients with LT and
  PST ≤ grade 1 showed average Lysholm score 91.2, average SSD 2.5 mm, and mean Tegner score decreased from
  6.9 (pre-injury) to 6.2. Patients who started the non-operative treatment within 2 weeks after injury revealed superior
  rates of grade 0 or 1 instability than those who commenced the treatment later than 2 weeks after injury (P =
  Conclusions: Implementing a non-operative treatment with brace in acute phase of ACL injury appears to be an
  effective and viable option to achieve a reasonable clinical outcome. We recommend earlier initiation of the non-
  operative treatment to obtain a better result in patients with acute ACL injury.
  Keywords: Non-operative treatment, Time of starting treatment, Acute injury, ACL, Knee

* Correspondence:;
  Department of Orthopedic Surgery, Samsung Medical Center,
Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu,
Seoul 06351, South Korea
  Stem Cell & Regenerative Medicine Institute, Samsung Medical Center, 81
Irwon-ro, Gangnam-gu, Seoul 06351, South Korea
Full list of author information is available at the end of the article

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Park et al. Knee Surgery & Related Research   (2021) 33:11                                                     Page 2 of 9

Introduction                                                  inclusion criteria for the initial non-operative treatment
An anterior cruciate ligament (ACL) injury is one of          for “acute ACL injury” were the followings: patients (1)
the most common significant knee injuries during              who had significant trauma to a previously uninjured
sports activities, however, the value of initial non-         knee within the preceding 4 weeks, (2) who presented
operative treatment for patients with acute ACL               with limitation of motion, swelling and/or effusion of
injury has not been properly recognized and is con-           the injured knee joint, and (3) whose diagnosis were
troversial [1–5]. ACL has primary healing potential           confirmed as ACL injury by magnetic resonance imaging
and there have been reports of spontaneous healing            (MRI). Increased signal intensity and swelling of ACL
of ACL after an injury, although the healing potential        substance on MRI was regarded as consistent with acute
is less in complete ruptures [6]. Therefore, proper           ACL injury [19] (Fig. 1). Patients who had previous his-
protection of the acutely injured ACL and ligament            tory of a substantial injury to either the affected knee or
and prevention of potential impairments may result in         the contralateral knee, or patients who required surgical
a good result in patients with acute ACL injury in            treatment due to combined ligament or meniscus injur-
patients with acute ACL injury. Actually, there were          ies were excluded. Consequently, the cohort of the
reports of true copers after non-operative treatment          present study initially consisted of 106 patients who met
even though it may not be a complete healing [7, 8].          the inclusion criteria. The cohort was prospectively
  The indication of non-operative treatment has been          followed up at regular intervals for a minimum of 12
known to include patients with partial tears, young chil-     months. Among them, 85 (80%) patients were available
dren with wide-open physes, and patients with low-risk        for regular follow-up and 21 (20%) patients were
activity levels, isolated ACL injuries, and mild pathologic   excluded (Fig. 2).
laxity [9]. Non-operative management includes a short           Our non-operative treatment program consisted of 6
period of immobilization, bracing, a progressive rehabili-    phases (Supplement 1). In phase I-III (from initial visit
tation program, and regular follow-up evaluations [1].        to 8 weeks), limited hinge brace was applied in order to
The various results of non-operative treatment of acute       prevent further injury, especially caused by pivot shifting
ACL injury previously reported may be due to the vari-        motion, protect blood clot formation, and reduce anteri-
ability of important parameters. The previous reports         orly displacing force on tibia. Range of motion exercise,
are from different inclusion criteria and treatment dura-     quadriceps setting and straight leg raising exercise were
tions, and interestingly, many of them actually did not       rigorously encouraged while wearing the brace. A
specifically describe the definition in terms of the acute-   gradual increase of exercise for improving muscle
ness of the ACL injury or the timing of initiating the        strength and endurance was implemented whilst main-
non-operative treatment [9–13]. Moreover, few studies         taining adequate protection to allow healing of the
analyzed both the ligamentous stability and functional        injured ACL (Phase IV; until 12 weeks). The strength
outcome after non-operative treatment of acute ACL in-        and sets of exercise were increased according to the
jury [14–18]. Furthermore, we could not find an article       capacity of each patient under the supervision of phys-
in the literature that compared the results from different    ical trainers. Upon successful completion of previous
timing of initiating the non-operative treatment after        phases, the non-operative treatment protocol proceeds,
acute ACL injury.                                             involving active rehabilitation and exercises that ultim-
  Therefore, the purpose of this study was to evaluate        ately prepare the patient to return to sports (Phase V-VI;
the ligamentous stability as well as the functional status    until 12 months). At the end of phase IV (at 12 weeks
of patients after non-operative treatment of acute ACL        into the protocol), the knee was examined with Lachman
injury, and to compare the outcome according to differ-       test (LT) and pivot-shift test (PST). If a hard endpoint
ent timing of initiating the treatment; within or later       was not palpable on LT or PST was positive of more
than 2 weeks after the injury (to determine if the onset      than grade 2, surgical intervention was recommended.
of treatment affects the outcome). We hypothesized that       Among them, the patients who wanted conservative
good ligament stability and functional status can be          treatment rather than surgery were categorized as coper
achieved through strict non-operative treatment pro-          and they proceeded to phase V-VI. Home exercise was
gram for an acute ACL injury; and the earlier the non-        continued and rehabilitation counseling was done ac-
operative treatment is commenced, the better the clin-        cording to the knee stability and muscle strength at out-
ical outcome can be obtained.                                 patient visits.
                                                                The clinical evaluation included LT, PST, Lysholm
Methods                                                       knee score, Tegner activity score and KT-2000 [20–22].
Two hundred and ninety eight patients with acute or           LT or PST was initially performed at the initial visit
chronic ACL injury were treated at our institution            within 4 weeks of the injury, then at 3 months and at 1-
between April 2008 and February 2013. Of these, the           year follow-up. The LT was graded as grade 0 (< 3 mm),
Park et al. Knee Surgery & Related Research        (2021) 33:11                                                                                  Page 3 of 9

 Fig. 1 Non-operative treatment was performed on the 28 year-old male patient with an acute anterior collateral ligament (ACL) injury that had
 occurred while playing soccer 1 week ago. a, b T2-weighted magnetic resonance (MR) sagittal image of the knee indicates a midsubstance ACL
 rupture. Initial physical examination was Lachman test grade 1 and pivot-shift test grade 1, and the Tegner activity score before the injury was 7.0. c, d
 T2-weighted MR image of the same patient treated non-operatively according to our program shows a well-healed ACL at 1 year after injury. At 2
 years after the injury, physical examination was Lachman test grade 0 and pivot-shift test grade 0, and the Tegner activity score was 7.0

 Fig. 2 Flow of participants detailing inclusion at 1-year follow-up. LT Lachman test, PST pivot-shift test, ACL anterior cruciate ligament
Park et al. Knee Surgery & Related Research       (2021) 33:11                                                                              Page 4 of 9

grade 1 (3-5 mm), grade 2 (6-10 mm), and grade 3 (> 10                        (1) and falling off a ladder (1). There were 27 patients
mm). The PST was graded as grade 0 (equal), grade 1                           (31%) with isolated ACL injury and 43 patients (50%)
(glide), grade 2 (clunk), and grade 3 (marked) [23, 24].                      with combined ligamentous injuries; medial collateral
The pre- and post-injury Tegner activity score was                            (36), posterior cruciate (2), lateral collateral (1), med-
assessed at initial visit and at the 1-year follow-up.                        ial collateral + posterior cruciate (2), and medial +
Lysholm knee score and side to side difference in anter-                      lateral collateral (2) ligaments. There were 31 patients
ior laxity by KT-2000 (MEDmetric, San Diego, CA) were                         (35%) who had combined meniscal injuries; medial
also evaluated at 1-year follow-up.                                           meniscus (20), lateral meniscus (8) and medial + lat-
  Statistical analyses were performed with the SPSS for                       eral meniscus (3) in the study cohort. Out of the 31
Windows 18.0 software package (SPSS Inc., Chicago, IL).                       patients with coexisting meniscal tears, 21 were
Fisher’s exact test was utilized to evaluate the treatment                    asymptomatic after the non-operative treatment of
results following the different timing of initiating the                      ACL, but 10 required arthroscopic meniscectomy or
treatment.                                                                    repair after the initial non-operative treatment to heal
                                                                              the ACL. Any patients who required acute surgical
Results                                                                       treatment (e.g. meniscal tears that require early
The final cohort of this study comprised 85 patients                          surgery such as displaced bucket handle tears) were
(64 males and 21 females) with a mean age of 35.8                             excluded from this study cohort (Patients belong to
years (range 18–59). The average activity level prior                         exclusion criteria).
to injury was Tegner activity score 7.0 (range 5–8).                            Initially, 84% of the patients showed LT and PST ≤
The most common cause of the injury was a sports                              grade 1, and 16% with ≥grade 2 (Fig. 3). The initial LT
injury; soccer (30 patients), non-sports slip (16),                           was grade 0 in 46 patients (54%), which improved to
skiing (15), basketball (5), martial arts (4), running                        grade 0 in 71 patients (84%) at 1-year follow-up. On
(4), traffic accident (2), badminton (2), tug-of-war (2),                     PST, 51 patients (60%) showed grade 0 initially, which
lacrosse (1), ice hockey (1), foot bolley ball (1), tennis                    improved to 63 patients (74%) at 1-year follow-up. As a

 Fig. 3 Distribution of patients according to Lachman test and pivot-shift test within 4 weeks after the anterior cruciate ligament (ACL) injury.
 Pivot-shift 0, pivot-shift test grade 0; Lachman 0, Lachman test grade 0
Park et al. Knee Surgery & Related Research             (2021) 33:11                                                                                         Page 5 of 9

Table 1 Comparison of the number of cases between the initial examination and at 1-year follow-up
                                   Lachman test                                                                  Pivot-shift test
                                   Initial                         At 1-year follow-up                           Initial                          At 1-year follow-up
Grade 0 (%)                        46 (54%)                        71 (84%)                                      51 (60%)                         63 (74%)
Grade 1 (%)                        26 (31%)                        13 (15%)                                      31 (36%)                         15 (17%)
Grade 2 (%)                        13 (15%)                        1 (1%)                                        3 (4%)                           5 (6%)
Grade 3 (%)                        0                               0                                             0                                3 (3%)
Total (%)                          85 (100%)                       85 (100%)                                     85 (100%)                        85 (100%)

whole, 77 patients (91%) showed LT and PST ≤ grade 1                                   the 14 patients with initial LT or PST ≥ grade 2, 11
(53 patients with both the LT and PST grade 0) at 1 year                               (79%) showed improved stability (Table 2).
follow-up (Table 1). Stability on physical examination                                   At 1-year follow-up, 77 (91%) out of the 85 patients
was maintained or improved in 68 (80%) of the 85                                       after the non-operative treatment did not receive recon-
patients in this study cohort. Of the 34 patients with                                 struction as copers (patients with LT and PST ≤ grade 1)
both LT and PST grade 0 initially, the stability was                                   and 8 (9%) patients required reconstruction (patients
maintained in 26 patients (76%) at 1-year follow-up. Of                                with LT or PST ≥ grade 2). Eight patients were

Table 2 Results of the non-operative treatment according to the initial Lachman and pivot-shift tests

L* Lachman test grade *, P* pivot-shift test grade * (i.e., P0L0 = pivot-shift test grade 0 and Lachman test grade 0).
(_): number of patients who underwent an anterior cruciate ligament (ACL) reconstruction described in parentheses. Patients undergoing ACL reconstruction were
examined prior to the surgery.
       : Patients initially with grade ≥ 2 instability on either Lachman test or pivot-shift test improved to grade ≤ 1 instability (both Lachman and pivot-shift test) at
1-year follow-up with non-operative treatment.
       : Patients initially grade ≥ 2 instability on either Lachman test or pivot-shift test remained at grade ≥ 2 instability (either Lachman or pivot-shift test) at 1-
year follow-up with non-operative treatment.
Park et al. Knee Surgery & Related Research             (2021) 33:11                                                                             Page 6 of 9

recommended to undergo an ACL reconstruction.                                          than grade 1 residual instability after the non-operative
Although 6 of the 8 patients underwent the ACL recon-                                  treatment, for whom we consequently recommended
struction, the remaining two patients, who had no com-                                 ACL reconstruction. Another important finding from
plaint of functional instability in their daily activities,                            the current study is that patients who initiated the non-
refused the surgery probably due to their low activity                                 operative treatment within 2 weeks after the ACL injury
demand or adaptation with activity modification (Fig. 2).                              showed better chance of resulting in both the LT and
  After the initial phase 1 treatment with a brace for 8                               PST ≤ grade 1. The high success rate of non-operative
weeks, 29 patients did not demonstrate a hard end point                                treatment in this study may be attributed to the consid-
on LT. They were advised to wear the brace for an                                      erable proportion of patients with LT0 and PS0 (62%).
additional 4 weeks. After the additional 4 weeks of bra-                               Due to swelling and effusion, instability could not be
cing, 12 showed improvement in stability, 15 indicated                                 confirmed at initial visit. Initial evaluation for stability
no change, and 2 demonstrated worsened stability.                                      was done within 4 weeks allowing time for swelling and
  Seventy-seven patients with LT and PST ≤ grade 1                                     effusion to subside. For patients who showed LT0/PS0
showed Lysholm score of average 91.2 (range, 68–100),                                  within 4 weeks, non-operative treatment protocol was
the average side to side difference of 2.5 mm (range,                                  continued. We suspect that a sizable proportion of
0.0–4.5), and the mean Tegner activity score was                                       patients with LT0 and PS0 probably had partial ruptures
decreased from 6.9 (range, 4–9) before the injury to 6.2                               rather than complete ruptures.
at 1-year follow-up (range, 4–8) (Table 3).                                               The natural history of ligament healing is similar to
  The comparison analysis of patients who initiated the                                other vascular soft tissues, occurring in three identifiable
non-operative treatment within or later than 2 weeks                                   stages: haemorrhage and inflammation, proliferation and
after the ACL injury revealed that there were more                                     scar formation, and remodeling. Each of the stages of
chance of resulting in both the LT and PST ≥ grade 2 in                                healing depends upon an adequate blood supply for the
patients with delayed initiation of the non-operative                                  delivery and removal of cells and metabolic substrates at
treatment (P = 0.043) (Table 4).                                                       the site of injury [25]. A number of studies found that
                                                                                       the epiligament is a donor of fibroblasts and other con-
Discussion                                                                             nective tissue cells, progenitor cells and blood vessels,
The results of this study shows that initial non-operative                             which migrate towards the body of the ligament via the
treatment of acute ACL injury implemented in acute                                     endoligament and play a key role in the process of liga-
phase (within 4 weeks after the injury) of ACL injury can                              ment repair [26]. Non-operative treatment initially per-
result in a reasonable success. Non-operative treatment                                formed by immobilization and protection using a brace
using a controlled motion brace initiated within 4 weeks                               is to avoid external factors that interfere with this heal-
of the injury showed 91% of both LT and PST ≤ grade 1                                  ing process. It was followed by a rehabilitation program
(62% with both LT and PST grade 0). Among them,                                        to recover joint motion, muscle strengthening, and activ-
decrease in Tegner activity score was less than 1. Only                                ity level. There is no evidence yet whether the non-
9% (8 patients) out of the 85 patients resulted in more                                operative treatment affected the healing process, and the

Table 3 Tegner activity score, Lysholm knee score, and side-to-side difference in anterior laxity by the KT-2000 arthrometer in
patients with both Lachman test and pivot-shift test ≤ grade 1
At 1-year follow-up                  P0L0                         P0L1                         P1L0                     P1L1            Total
                                     (n = 53, 100%)               (n = 6, 100%)                (n = 17, 100%)           (n = 1, 100%)   (n = 77, 100%)
Changes of the Tegner activity score
  Improved                           0                            0                            0                        0               0
  Maintained                         27 (51%)                     5 (83%)                      7 (42%)                  0               39 (51%)
  Decreased (− 1 level)              17 (32%)                     1 (17%)                      5 (29%)                  1 (100%)        23 (30%)
  Decreased (− 2 level)              8 (15%)                      0                            5 (29%)                  0               14 (18%)
  Decreased (− 3 level)              1 (2%)                       0                            0                        0               1 (1%)
Tegner activity score
  Pre-injury                         6.7 (range, 4–8)             7.3 (range, 7–8)             7.3 (range, 5–9)         8.0             6.9 (range, 4–9)
  Last follow-up                     6.0 (range, 4–8)             7.2 (range, 7–8)             6.4 (range, 5–8)         7.0             6.2 (range, 4–8)
Lysholm knee score                   91.2 (range, 72–100)         91.2 (range, 85–100)         91.4 (range, 68–100)     85              91.2 (range, 68–100)
Side-to-side difference (mm)         2.2 (range, 0–4.5)           2.8 (range, 1–4.5)           3.2 (range, 1.5–4.5)     4.5             2.5 (range, 0–4.5)
L* Lachman test grade *, P* pivot-shift test grade * (i.e., P0L0 = pivot-shift test grade 0 and Lachman test grade 0)
Park et al. Knee Surgery & Related Research            (2021) 33:11                                                                      Page 7 of 9

Table 4 Distribution of patients with both Lachman and pivot-shift test ≤ grade 1 according to the time of initiating the non-
operative treatment
Initial                  Lachman and pivot-shift ≤ G1(at 1-year follow-up) according to the time of initiating the treatment
                         < 1 week                      1 ~ < 2 weeks                  2 ~ < 3 weeks                   3 ~ < 4 weeks
test and
pivot-shift test
L0P0 (n = 34)            11/11 (100%)                  10/10 (100%)                   4/4 (100%)                      9/9 (100%)
L0P1 (n = 12)            2/2 (100%)                    0/0                            3/3 (100%)                      6/7 (85%)
L1P0 (n = 12)            4/4 (100%)                    5/5 (100%)                     1/1 (100%)                      2/2 (100%)
L1P1 (n = 13)            3/4 (75%)                     3/3 (100%)                     1/2 (50%)                       2/4 (50%)
L0P2 (n = 0)             0/0                           0/0                            0/0                             0/0
L2P0 (n = 5)             4/4 (100%)                    0/0                            0/0                             0/1 (0%)
L1P2 (n = 1)             1/1 (100%)                    0/0                            0/0                             0/0
L2P1 (n = 6)             4/4 (100%)                    0/0                            0/0                             1/2 (50%)
L2P2 (n = 2)             1/1 (100%)                    0/0                            0/1 (0%)                        0/0
Total (n = 85)           30/31 (96.8%)                 18/18 (100%)                   9/11 (81.8%)                    20/25 (80.0%)   P = 0.043
L* Lachman test grade*, P* pivot-shift test grade* (i.e., P0L0 = pivot-shift test grade 0 and Lachman test grade 0)

protocols used in previous studies have been tried in                                non-operative treatment using a controlled motion
various ways without a specific guideline [1].                                       brace that showed improvement of ligament laxity and
   There are some previous papers that reported satisfac-                            restoration of their continuity on MRI. However, they
tory results of an injured ACL using non-operative treat-                            did not specifically describe the inclusion criteria of
ment. Ageberg et al. [14] and also Nueman et al. [13]                                their non-operative treatment in terms of the “acute-
reported that a well-constructed rehabilitation program                              ness” of the ACL injury as well as the timing of initiat-
with non-operative treatment resulted in satisfactory                                ing the non-operative treatment. Moreover, they just
clinical outcomes after 15 years of follow-up. Ageberg                               included patients with mild instability (LT 0 or 1) at
et al. [14] also reported that 65 ~ 85% of 100 patients                              initial visits and excluded patients with MRI findings
treated non-operatively demonstrated limb symmetry                                   suggesting complete rupture of ACL. Considering the
index of higher than 90%. However, both studies had the                              limited accuracy in distinguishing whether the ACL in-
inclusion criteria of within 5 days of the ACL injury,                               jury is partial or complete by MRI in acute stage of
which seem to represent a too limited percentage of pa-                              ACL injury, and the difficulty in precisely assessing the
tients in a real clinical setting. They also lacked the                              stability at the acute stage of ACL injury [9, 27, 28], we
evaluation on restoration of the stability of ACL directly                           think that their study seems to have a significant limita-
by KT-2000, LT or PST. Unlike these two studies, our                                 tion. As we included every consecutive patient in a
protocol used a controlled motion brace during the                                   non-selective manner, we believe the strategy and result
treatment period, providing proper protection to the in-                             of the present study is more practical and informative.
jured ACL. We agree that injured ACL has healing po-                                 By the way, even in the cohort of this study, majority of
tential as mentioned by these studies, and we suggest                                patients showed mild instability initially, we admit that
that use of controlled motion brace could expand non-                                most of them should have had partial tear of the ACL.
operative treatment to patients within 4 weeks after the                               In the present study, patients who initiated the
injury. The result of the present study shows that a                                 non-operative treatment within 2 weeks after the ACL
proper protection initiated within 4 weeks of ACL injury                             injury showed better chance of resulting in both the
followed by careful rehabilitation can result in a good                              LT and PST ≤ grade 1. This result shows that the
clinical outcome.                                                                    time of initiating the non-operative treatment is an
   Since it is difficult to differentiate partial versus                             important factor affecting the clinical outcome.
complete tears by MRI or physical examination at acute                               Because previous reports on the non-operative treat-
phase of ACL injury, we think that treating the two                                  ment did not specify when the non-operative treat-
groups differently at acute stage of ACL injury is not                               ment was commenced, we believe the result of this
possible in an actual clinical setting [9, 27, 28]. Neusel                           study is significant by suggesting the guideline in
et al. [18] reported that good to satisfactory results                               terms of the timing of initiation of the non-operative
were shown in cases of partial rupture, but the results                              treatment. We could consider initiating the non-
were limited to isolated ACL injuries. Ahn et al. [10] re-                           operative treatment as soon as possible based on the
ported a short term result of acute ACL injury after                                 result of this study.
Park et al. Knee Surgery & Related Research   (2021) 33:11                                                                          Page 8 of 9

   The result of this study provides a rough prognosis of       up after the initial 3 month non-operative treatment
treatment according to the initial status of the knee after     period (Fig. 2). For this study, we made great efforts to
the acute ACL injury. Patients who initially showed both        contact the 21 patients lost to follow-up, which found
the LT and PST grade 0 had higher propensity to show            that 5 underwent ACL reconstruction surgery at other
LT and PST ≤ grade 1 after the non-operative treatment          hospital before completion of our initial non-operative
than the patients with initial LT or PST ≥ grade 2. How-        treatment program, another 11 did not show any symp-
ever, even among the 14 patients with initial LT or             toms of instability, and 5 were unreachable. Fourth, we
PST ≥ grade 2, 11patients (79%) showed improved                 presented the instability degree using KT-2000 as an ob-
results with LT and PST ≤ grade 1. This finding suggests        jective test for evaluating the recovery of injured liga-
that there could have been a remodeling of the injured          ments. The lack of more objective results was a
ACL along with the healing of the injured site. Kosto-          limitation of this study because we did not present
giannis et al. [16] reported that a positive PST at 3           followed-MRI results that can be displayed as images.
months after injury is the strongest predictor for the
need of reconstruction. We agree with their conclusion          Conclusion
and we believe that the need of an ACL reconstruction           Implementing a non-operative treatment with brace in
should be determined after proper non-operative treat-          acute phase of ACL injury appears to be an effective and
ment in acute stage of ACL injury. In a randomized              viable option to achieve a reasonable clinical outcome.
controlled trial, Frobell et al. [2] demonstrated that a        We recommend earlier initiation of the non-operative
strategy of rehabilitation plus early ACL reconstruction        treatment to obtain a better result in patients with acute
did not result in better outcome than a strategy of re-         ACL injury.
habilitation plus optional delayed ACL reconstruction
after 2 years of follow-up. They emphasized that more           ACL: Anterior cruciate ligament; MRI: Magnetic resonance imaging;
than half the ACL reconstruction could be avoided with-         LT: Lachman test; L*: Lachman test grade *; PST: Pivot-shit test; P*: Pivot-shift
out adversely affecting outcomes when the latter strategy       test grade *; SSD: Side to side difference
is utilized. We believe the result of the present study
supports their conclusion. Moreover, many of the pa-            Supplementary Information
                                                                The online version contains supplementary material available at https://doi.
tients in present study were able to return to their pre-
injury activity level or had a slight decreased activity,
which is consistent with the reports of Kostogiannis             Additional file 1: Supplement 1. Non-operative treatment protocol for
et al. [16] and Neuman et al. [17]. Therefore, we believe        acute ACL injury in SMC (Samsung Medical Center) Knee Clinic (version
that in most patients with leisure sports activities, deter-     1.0.)
mination of the necessity of surgical reconstruction of
ACL would better be made after completion of initial            Acknowledgements
                                                                This work was carried out with the support of “a grant of the Korea Health
non-operative treatment in acute stage of ACL injury.           Technology R&D project through the Korea Health Industry Development
   Some limitations of our study need to be addressed.          Institute (KHIDI), supported by the Ministry of Health and Welfare, Republic
First, we need to address that the initial instability of the   of Korea (HI14C3484). The funding sources were not involved in the study
                                                                design, collection, analysis or interpretation of the data, writing of the
study cohort was biased to low or moderate grade in LT          manuscript, or in the decision to submit the manuscript for publication.
and PST. There were relatively small numbers of pa-
tients (17% of the study cohort) with instability of more       Authors’ contributions
                                                                YGP wrote the manuscript and performed data collection and data
than LT or PST grade 1. Since patients with instability         interpretation. CWH designed and performed the study, and wrote the
of less than LT or PST grade 2 would likely have been           manuscript. YBP and SEN performed literature search, data collection, made
partial tears, we assumed that the proportion of partial        figure, and helped to write the manuscript. MK, TSK and YYC performed
                                                                literature search, data interpretation, and help to write the manuscript. The
tear was high in this study cohort. Second, we cannot           authors read and approved the final manuscript.
guarantee that the long term clinical outcome of the pa-
tients with grade 1 instability without surgery will be         Funding
                                                                No funding was received in preparation of this manuscript.
well. However, Neuman et al. [17] reported that a low
grade ACL injury appears to result in a successful out-         Availability of data and materials
come without secondary knee surgery or knee osteoarth-          The datasets generated and/or analyzed during the current study are not
ritis in 15 years. Third, 21 patients (20%) out of the          publicly available due to protection patients` information but are available
                                                                from the corresponding author on reasonable request.
initial cohort of 106 patients were lost to follow-up.
Thirteen patients were lost in follow-up during the ini-        Declarations
tial three months period of the non-operative treatment,
                                                                Ethics approval and consent to participate
2 patients failed in the regular use of a controlled mo-        All procedures performed in studies involving human participants were in
tion brace, and 6 patients were gone missing in follow-         accordance with the ethical standards of the institutional and/or national
Park et al. Knee Surgery & Related Research            (2021) 33:11                                                                                        Page 9 of 9

research committee and with the 1964 Helsinki declaration and its later                  systematic review. Sports Med 37(8):703–716.
amendments or comparable ethical standards. This study was approved by                   56-200737080-00004
institutional review board of Samsung Medical Center (IRB file No.2011–01–         13.   Neuman P, Englund M, Kostogiannis I, Friden T, Roos H, Dahlberg LE (2008)
061-002).                                                                                Prevalence of tibiofemoral osteoarthritis 15 years after nonoperative
                                                                                         treatment of anterior cruciate ligament injury: a prospective cohort study.
                                                                                         Am J Sports Med 36(9):1717–1725.
Consent for publication
Informed consent was obtained from patient included in the study.
                                                                                   14.   Ageberg E, Pettersson A, Friden T (2007) 15-year follow-up of
                                                                                         neuromuscular function in patients with unilateral nonreconstructed
Competing interests                                                                      anterior cruciate ligament injury initially treated with rehabilitation and
The authors have no conflict of interest to declare.                                     activity modification: a longitudinal prospective study. Am J Sports Med
Author details                                                                     15.   Kostogiannis I, Ageberg E, Neuman P, Dahlberg L, Friden T, Roos H (2007)
1                                                                                        Activity level and subjective knee function 15 years after anterior cruciate
 Department of Orthopedic Surgery, Jeju National University Hospital, Jeju
National University School of Medicine, Aran 13gil 15, Jeju-si, Jeju                     ligament injury: a prospective, longitudinal study of nonreconstructed
Self-Governing Province 63241, South Korea. 2Department of Orthopedic                    patients. Am J Sports Med 35(7):1135–1143.
Surgery, Samsung Medical Center, Sungkyunkwan University School of                       6507299238
Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 06351, South Korea. 3Stem Cell &          16.   Kostogiannis I, Ageberg E, Neuman P, Dahlberg LE, Friden T, Roos H (2008)
Regenerative Medicine Institute, Samsung Medical Center, 81 Irwon-ro,                    Clinically assessed knee joint laxity as a predictor for reconstruction after an
Gangnam-gu, Seoul 06351, South Korea. 4Department of Health Sciences and                 anterior cruciate ligament injury: a prospective study of 100 patients treated
Technology, SAIHST, Sungkyunkwan University, 81 Irwon-ro, Gangnam-gu,                    with activity modification and rehabilitation. Am J Sports Med 36(8):1528–
Seoul 06351, South Korea. 5Department of Orthopedic Surgery, Chung-Ang                   1533.
University Hospital, Chung-Ang University College of Medicine, 102                 17.   Neuman P, Kostogiannis I, Friden T, Roos H, Dahlberg LE, Englund M (2012)
Heukseok-ro, Dongjak-gu, Seoul 06973, South Korea. 6Department of                        Knee laxity after complete anterior cruciate ligament tear: a prospective
Orthopedic Surgery, Asan Teun Teun Hospital, 593 2-dong, Sangrok-gu,                     study over 15 years. Scand J Med Sci Sports 22(2):156–163.
Ansan-si, Gyeonggi-do 15512, South Korea. 7Department of Orthopedic                      0.1111/j.1600-0838.2010.01157.x
Surgery, Wiltse Memorial Hospital, 560 Gyeongsu-daero, Dongan-gu,                  18.   Neusel E, Maibaum S, Rompe G (1996) Five-year results of conservatively
Anyang-si, Gyeonggi-do 14112, South Korea.                                               treated tears of the anterior cruciate ligament. Arch Orthop Trauma Surg
Received: 2 November 2020 Accepted: 10 March 2021                                  19.   Klass D, Toms AP, Greenwood R, Hopgood P (2007) MR imaging of acute
                                                                                         anterior cruciate ligament injuries. Knee. 14(5):339–347.
                                                                                   20.   Kong DH, Yang SJ, Ha JK, Jang SH, Seo JG, Kim JG (2012) Validation of
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